1. Studies by Hargrave and Geen estimated natural community grazing ratesby measuring feeding rates of individual zooplankton species in the laboratoryand then computing community grazing rates for field conditions using the knownpopulation density of grazers.
By以前结构无需解释,by以后有两个作介词宾语短语的动名词结构,measuring和后面表示并列和顺接的andthen之后的computing,说的是计算方法;前一个measuring说的是先算出实验室中浮游动物品种的单位捕食速率,后面的computing前其实省略了一个by,而且在这个动名词结构中还包括一个分词结构using the known population density ofgrazers,用已知的捕食者的种群密度计算出其野外的群体捕食速率。整个的by以后的计算过程简单了就是:实验室单位速率×野外密度=野外群体速率。